Coil for magnetic stimulation

ABSTRACT

A magnetic stimulator, which may be used as a transcranial magnetic stimulation (TMS) device, and a method for its use are disclosed. The stimulator comprises a frame and an electrically conductive coil having a partially toroidal or ovate base and an outwardly projecting extension portion. The frame may be a flexible or malleable material and may be non-conductive. The electrically conductive coil may comprise one or more windings of electrically conductive material (such as a wire) coupled to the frame. The coil is electrically connected to a power supply. The device may be placed adjacent to or in contact with the body of a subject, such as on the head of a subject. The device may be used on humans for treating certain physiological conditions, such as cardiovascular or neurophysiological conditions, or for studying the physiology of the body. This device is useful in studying or treating neurophysiological conditions associated with the deep regions of the brain, such as drug addiction and depression.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Stage of International Application No.PCT/US01/50737, filed Oct. 19, 2001, which was published in Englishunder PCT Article 21(2) and which claims the benefit of U.S. ProvisionalApplication No. 60/242,297, filed Oct. 20, 2000. Both applications areincorporated herein in their entirety.

FIELD

This invention relates to coils for magnetic stimulation, particularlytranscranial magnetic stimulation, and more particularly to transcranialmagnetic stimulation capable of stimulating deep regions of the brain.

BACKGROUND

Electromagnets are capable of inducing electric fields in mostbiological tissues. Transcranial magnetic stimulation (TMS) is widelyused as a research tool to study aspects of the human brain, includingmotor function, vision, language, and brain disorders. Additionally,therapeutic uses of magnetic stimulation devices, particularly inpsychiatry, currently are being investigated.

Magnetic stimulation of biological tissue may be accomplished by passinga brief, high-current electric pulse through a coil of electricallyconductive material, such as a wire positioned adjacent tissue to bestimulated. A magnetic field is produced by the electric pulse withlines of flux passing perpendicularly to the plane of the magnetic coil.This magnetic field, in turn, can induce an electric field in aconductive medium. An animal brain is a conductive medium and in TMS,the induced electric field stimulates the neurons of the brain. However,an electromagnetic coil may be placed over other parts of the body tostimulate other electrically conductive tissues, such as muscle.

Functional magnetic coils may be produced in a variety of shapesincluding circles, FIG. 8's, squares, petals, spirals, and “slinky”coils. See, e.g. Caldwell, J., Optimizing Magnetic Stimulator Design,Magnetic Motor Stimulation: Basic Principles and Clinical Experience,1991, 238-48 (ed. Levy, W. J., et al.); Zimmermann, K. P., and Simpson,R. K., Electroencephal. Clin. Neurophysiol., 101:145-52 (1996); U.S.Pat. No. 6,066,084 (Edrich et al.). The coils may include features otherthan a coil of a transducing material. For example, U.S. Pat. No.6,086,525 (Davey et al.) and WO 98/06342 (Epstein et al.) disclosemagnetic stimulators made from coil windings around a core offerromagnetic material, preferably vanadium permendur. However, suchcoils can be quite heavy and expensive to manufacture.

TMS using known coils has been shown to be able to stimulate the regionsof the brain close to the surface of the skull, but magnetic fieldsproduced by these known coils generally do not penetrate deeply into thebrain, unless the intensity of the magnetic field is greatly increased.However, increasing the strength or intensity of the magnetic fieldcarries a risk of causing physiological damage and seizures.

The deep regions of the brain include the nucleus accumbens, a portionof the brain that plays a major role in rewarding circuits and is knownto be activated in response to doses of cocaine. Additionally, neuronalfibers connecting the medial, prefrontal, or cingulate cortex with thenucleus accumbens have a role in reward and motivation, and activationof the nucleus accumbens also may cause hedonic effects.

Known coils used for TMS (e.g., a figure eight coil) affect the corticalregions of the brain, primarily the cortical region under the center ofthe coil. However, the intensities of the electric fields produced bythese known coils decrease very rapidly with increasing distance fromthe coil. Therefore, stimulating deep regions of the brain using knowncoils would require either invading the skull (and often the brain) withthe coil, or using a high intensity electric field. Invasive techniquesoften cause the subject or patient to experience pain or discomfort, andwould usually be avoided by the patient. High intensity electric fieldsmay cause epileptic seizures or other neurological problems. Moreover,high intensity electric fields may cause generalized effects throughouta subject's brain, rather than stimulating a specific deep region of thebrain, and may cause other harmful side effects. Additionally, themaximum field intensity can be limited by known coil designs.

Therefore, a need exists for a magnetic coil capable of stimulating thedeep regions of the brain when placed outside the skull duringnon-invasive TMS.

SUMMARY

The present invention relates to a coil for magnetic stimulation. Thecoil may be placed externally of a body part of a subject and, when soplaced, is operable to induce electric currents within the body of thatsubject. The magnetic coil may be used as a transcranial magneticstimulation (TMS) device and is capable of stimulating the deep regionsof the brain, such as the nucleus accumbens.

The device comprises a frame and an electrically conductive coil, whichmay have a partially toroidal or ovate base and an outwardly projectingextension portion. The partially toroidal or ovate base has a concavefirst side that is usually directed toward the body of the subject. Theextension portion extends from the second side of the base (i.e., awayfrom the concave first side). The frame may be a flexible or malleablematerial, and the electrically conductive coil may comprise one or morewindings of electrically conductive material (such as a wire) coupled tothe frame. The coil is electrically connected to a power supply.

Particular embodiments use a power supply capable of producing a rate ofcurrent change in the range of about 10,000 amperes per 100 microsecondsor higher to produce an electric field within the biological tissue,such as the brain, in a range from about 10 to about 100 volts per meteror higher. The coil may be activated by one or more pulses of electriccurrent, with a pulse generally lasting about 1000 microseconds.

The device may be placed adjacent to or in contact with the body of asubject (such as an animal). In particular embodiments, the device isplaced on top of the head of a human subject. However, the apparatuscould be placed anywhere on the body of a subject and used tomagnetically stimulate a tissue or multiple tissues of that subject'sbody, such as by inducing electric fields within such tissues. If thedevice is placed externally to the skull of the subject, the device maybe placed in various orientations around the skull.

The device has a base portion with a first end, a second end, a lengthaxis, and a width axis. In some embodiments, the configuration of thebase comprises an arch along each axis. This arch configuration (alongboth the length and width axes) is generally complementary to theexternal shape of the body part with which the device is used, andcomprises a generally toroidal or ovate shape.

The overall length of the base (as measured along the length axis) canbe adapted to a particular subject or class of subjects, depending onthe size of the subject and location on the body where the device willbe placed. A device with an arch length along the length axis of thebase of about 26 centimeters has been found suitable for use with mostadult humans, if the device is to be placed externally to the skull ofthe subject. Additionally, the overall width of the partially toroidalor ovate base (as measured along the width axis) can be adapted to aparticular subject or class of subjects, depending on the size of thesubject and location on the body where the device will be placed. Foradult human subjects, the device may have an arch length along the widthaxis in the range of about 5 centimeters, if the device is to be placedexternally of the skull of the subject.

The extension portion provides a return path for the flow of electricitythrough the partially toroidal or ovate base. In some embodiments, theextension has a minimal number of components extending radially of thebase in order to reduce opposition to or interference with the magneticfields produced by the coil portions in the base. A particularembodiment accomplishes this objective by using a triangular, orupwardly converging, extension. However, the extension may form shapesother than triangular—such as arcuate, or hemispherical—so long as theextension provides reduced radial components and reduces interferencewith the magnetic fields produced by the coil in the base.

In alternative embodiments, the extension comprises a collection ofindividual return paths in the form of elongated elements projectingradically outwardly from the base portion. For example, the extensionmay include a number of return paths (corresponding to individual wires)arranged in a fan-like pattern. In such embodiments, the individualreturn paths optionally may be offset in a forward or rearwarddirection.

The coil comprises one or more windings of an electrically conductivematerial, such as a metal band or wires that function as electricaltransducers. In some embodiments, the windings are associated with theframe. For example, wire may be run alongside of, mounted to, woundaround, or placed inside the frame, so long as the frame is notelectrically conductive. In other embodiments, the frame itself is thecoil. The device coil also may comprise other electrical components,such as resistors and capacitors.

The magnetic stimulator also may include a cushion placed adjacent tothe first side of the base, which faces the subject. The device also maycomprise some nonconductive material, such as plastic or rubber, thatencases the frame and coil, and may employ a frame made from someflexible or malleable material. Particular embodiments use a flexible ormalleable base in order to allow the user to better align the coil andallow some portions of the coil to lie tangential to the body surface ofthe subject.

The device can be used in a variety of ways and on any part of subject'sbody. Any conductive tissue, including (but not limited to) nervoustissue and muscle tissue, may be stimulated by the device.

The device may be used on humans for treating certain physiologicalconditions, such as neurophysiological conditions, or for studying thephysiology of the body. For example, the device may be used to study ortreat neurophysiological conditions associated with the deep regions ofthe brain, such as drug addiction and depression.

One embodiment of the method for using the device comprises identifyinga subject suffering a neurophysiological condition; providing anelectrically conductive coil as described above (i.e., having apartially toroidal or ovate base with a concave first side to bedirected toward a body part of the subject); placing the coil externalto the subject's skull; electrically connecting a power supply to thecoil; and activating the coil to stimulate the deep region of thesubject's brain. The device may be used in combination with brainimaging, such as magnetic resonance imaging (MRI) or positron emissiontomography (PET), to study the effect of deep brain stimulation on otherregions of the brain. Many embodiments comprise non-invasivelystimulating a subject's brain.

In some embodiments, a train of electromagnetic pulses is administeredto the subject. The pulse train may comprise an appropriate number ofindividual pulses administered over a certain period of time. The numberand frequency of pulses may vary. Certain embodiments use a frequencyrange of about 20 to about 30 Hz. The train of pulses may beadministered during a certain period of time, such as from about 20 toabout 30 seconds. Plural trains of magnetic pulses also may beadministered at a single session. If the subject is suffering a specificcondition, multiple treatment sessions may be conducted until clinicalimprovement occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of one embodiment of the deviceplaced on the head of a human.

FIG. 2 illustrates an electrical diagram for a magnetic coil embodied inthe device shown in FIG. 1.

FIG. 3 illustrates a frontal view of the device of FIG. 1.

FIG. 4 illustrates a side view of the device of FIG. 1.

FIG. 5 illustrates an enlarged cross-section through the device shown inFIG. 1, taken at line 5-5.

FIG. 6. is a graph comparing field strengths of a known coil with asingle winding of the coil in the embodiment illustrated in FIGS. 1 and2.

FIG. 7 is a graph comparing the field strengths of a single winding andthe entire set of windings of the coil in the embodiment illustrated inFIGS. 1 and 2.

FIG. 8 is a perspective view of a second embodiment of the device placedon the head of a human.

FIG. 9 is a frontal view of the device of FIG. 8.

FIG. 10 is a side view of the device of FIG. 8.

FIG. 11 is a partial schematic of the flow of electricity through thewindings of the device illustrated in FIGS. 8-9. This schematic is notan electrical circuit diagram. For clarity, only a few of the radiallyextending elements are shown.

FIG. 12 is a graph comparing theoretical calculations and actualmeasurements of electric field strength for the embodiment illustratedin FIGS. 8-10.

FIG. 13 is a graph comparing theoretical calculations and actualmeasurements of electric field strength, relative to the maximal fieldstrength in the brain cortex, for the embodiment illustrated in FIGS.8-10.

DETAILED DESCRIPTION

As used herein, the singular forms of “a,” “an,” and “the,” refer toboth the singular as well as plural, unless the context clearlyindicates otherwise. For example, the term “a coil” includes singular orplural coils and can be considered equivalent to the phrase “at leastone coil.”

As used herein, the term “comprises” means “includes.”

The present invention relates to a coil for magnetic stimulation that,when placed externally of a body part of a subject, is operable toinduce electric currents within the body of that subject. In particularembodiments, the magnetic coil may be used for transcranial magneticstimulation (TMS). If placed outside the skull of a subject, the deviceis capable of stimulating the brain of the subject, including the deepregions of the brain, such as the nucleus accumbens. Methods for usingthis device include treating neurophysiological conditions, such asclinical or non-clinical depression, substance abuse, and drugaddiction.

FIG. 1 shows one embodiment of the device. The device 11 comprises aframe and an electrically conductive coil having a partially toroidal orovate base 12 and an outwardly projecting extension portion 14. In someembodiments, the frame itself is the electrically conductive coil, suchas a frame composed of electrically conductive material. In otherembodiments, however, the frame is a flexible or malleable material,which may be configured to a desired shape for a specific application,and the electrically conductive coil comprises one or more windings ofelectrically conductive material associated with the frame, such asbeing run alongside of, mounted to, wound around, or placed inside theframe.

The coil is electrically connected to a power supply (not shown), suchas by electrical leads 16, 18 in FIG. 1. Other embodiments may employ asimilar connection to a power supply via similar electrical leads.

The coil may be composed of any electrically conductive material, suchas metal. Particular embodiments have coils comprising wire made ofcopper, aluminum, or other electrically conductive material. The powersupply may be any appropriate commercially available power supply, suchas the power supplies available for use with other magnetic coils.Examples of such power supplies include those sold with various modelsof magnetic stimulators produced by Medtronic, Inc. of Minneapolis,Minn., USA (e.g., MagPro, MagLite Compact), or power supplies sold withvarious models of magnetic stimulators produced by Magstim Company US,LLC, of New York, N.Y., USA (e.g., Magstim Model 200, Magstim Model 220,Magstim Model 250, BiStim, Magstim Rapid, Magstim QuadroPulse).

Particular embodiments use a power supply capable of producing a rate ofcurrent change in the range of about 10,000 ampere per 100 microsecondsor higher, depending on coil inductance, to produce an electric field ina range from about 10 to about several hundred volts per meter. The coilmay be activated by one or more pulses of electric current, with eachpulse lasting up to about 2000 microseconds. In particular embodiments,the pulse length is about 1000 microseconds in duration.

For stimulating nerve tissue, such as brain tissue, maximal current andthe rise of time of the current at the beginning of the pulse largelydetermine the pulse length. These parameters largely depend on the powersupply used to generate the electrical pulse and the inductance of thecoil. In some embodiments, one turn of the coil has an inductance ofabout 10 microhenri. A commercially available power supply (describedabove) can generate an electrical pulse in the coil having a pulselength of about 1000 microseconds. However, the pulse length may bealtered by changing the capacitance and/or resistance in the circuit,and/or the inductance or resistance of the coil.

The partially toroidal or ovate base 12 has a concave first, or outer,side 19, which is directed toward the body part of the subject, and asecond, or inner, side 20 opposite first side 19. The extension portion14 extends outwardly from this second side 20 and away from the base.

The device may be placed adjacent to or in contact with the body of asubject. FIG. 1 illustrates placement of the device 11 on the top of thehead 100 of a human subject. However, the apparatus could be placedanywhere on the body of a subject and used to magnetically stimulatetissues of that subject's body, such as by inducing electric fieldswithin such tissues. Additionally, the subject may be any animal, suchas a mammal including a human.

If the device is placed externally of the skull of the subject, thedevice may be placed in various orientations around the skull. Forexample, FIG. 1 shows the device 11 placed on top of the skull. Thedevice 11 could be placed at the back of the skull, across the subject'sforehead, or elsewhere on the skull. However, the device 11 effectivelyinduces electric fields within the body of a subject when the device 11is placed with the concave side 19 of the base 12 facing the body of thesubject.

The device 11 pictured in FIG. 1 has a partially toroidal or ovate base12 with a first end 22 and a second end 24. A line extending betweenthese two ends 22, 24 defines a length axis along the length of the base12. The base 12 has a substantially arcuate, semi-circular or semi-ovateshape along its length axis, as further illustrated in FIG. 3. The base12 also has a width axis extending perpendicular to its length axis andthis width axis has a substantially arcuate, semicircular or semi-ovateshape as further illustrated in FIG. 4. Thus, the base 12 pictured inFIG. 1 comprises an arch extending along its length axis and an archextending along its width axis.

In the illustrated embodiment, the arch configurations along both thelength and width axes are complementary to the external shape of thebody part with which the device is to be used. In the illustratedembodiment, the device conforms to the side-to-side and front-to-backarch shape of a subject's skull.

The extent of the base 12 can be described in terms of degrees ofrotation or distance in length. The length axis of the base 12 extendsless than about 360 degrees, such as extending less than about 270degrees. For example, the length axis of the base 12 of the deviceillustrated in FIGS. 1 and 3 extends about 180 degrees in rotation. Theoverall length of the base (as measured along the length axis) can beadapted to a particular subject or class of subjects, depending on thesize of the subject and where on the body the device will be placed.Some embodiments of the device have an arch length along the length axisof the base in a range of from about 10 to about 50 centimeters. Foradult human subjects, the device may have an arch length along thelength axis of the base in a range of from about 20 to about 30centimeters. A device with an arch length along the length axis of thebase of about 26 centimeters has been found sufficient for use with mostadult humans, if the device is to be placed externally to the skull ofthe subject.

Similar to the length axis, the width axis of the base 12 extends lessthan 360 degrees, such as extending less than about 270 degrees, lessthan about 180 degrees, or even less than about 90 degrees. For example,the width axis of the base 12 of the device illustrated in FIGS. 1 and 4extends about 45 degrees in rotation.

Additionally, the overall width of the base (as measured along the widthaxis) can be adapted to a particular subject or class of subjects,depending on the size of the subject and where on the body the devicewill be placed. Some embodiments of the device have an arch length alongthe width axis in a range of from about 2 to about 15 centimeters. Foradult human subjects, the device may have an arch length along the widthaxis in the range of about 5 centimeters, if the device is to be placedexternally to the skull of the subject.

The extent of the base—whether measured in degrees of rotation about, ordistance in length along, either the length axis or width axis—can beadapted to fit a particular subject or method of use, so as long as thebase remains substantially toroidal or ovate. For example, the concavefirst side 19 of the base 12 can be configured to be complementary tothe cranium of a subject.

The extension 14 provides a path for the flow of electricity to and fromthe base 12. In the embodiment illustrated in FIGS. 1-4, the extensionhas two components extending radially of the base in order to reducecreation of a surface charge in the subject's tissue, such as a surfacecharge on the brain of the subject. This surface charge can interferewith and reduce the strength of the electric field produced by the coilportions in the base. The embodiment of FIG. 1 accomplishes thisobjective by using a triangular, or upwardly converging, extension 14.The extension 14 comprises first and second elongated elements, 26, 28.The elements have a first set of inner ends 30, 32 connected to the base12 at positions spaced apart along the length axis of the base 12. InFIG. 1, the first elongated element 26 has a first inner end 30connected to the base 12 adjacent to the first end 22 of the base 12,and the second elongated element 28 has a first inner end 32 connectedto the base 12 adjacent to the second end 24 of the base 12. Theremainder portions 34, 36 of these elements 26, 28 extend away from thebase 12 and converge toward each other.

In the embodiment of FIG. 1, the first and second inner ends 30, 32 areinterconnected through a central portion of base 12 to form a triangularshape. This triangular shape is further illustrated by FIG. 3. However,the extension may form shapes other than triangular—such as arcuate orhemispherical—so long as the extension provides reduced radialcomponents and reduces interference with the electric fields produced bythe coil in the base 12. For example, the triangular extension portion14 allows the current flow through electrical conductors in theextension portion 14 to reach the base 12 at an orientationsubstantially tangential to the body part of the subject, such as theskull of the human pictured in FIGS. 1 and 3. A similar substantiallytangential relationship between the extension portion and the body partof the subject may be accomplished by extension portions having othershapes as well.

The extension portion also may comprise a unibody element, rather thanseparate elements. For example, a device similar to the embodimentillustrated in FIGS. 1 and 3 could be made using a unibody extensionelement rather than the two separate elongated elements 26, 28. Theextension portion also may comprise three or more elements.Additionally, the extension may be centered over the base, or placedoff-center relative to the base.

If a triangular extension portion is used (whether a unibody element orcomprised of plural elements), this triangular portion will comprisethree interior angles. For example, the extension portion illustrated byFIG. 1 (discussed above) has a first angle formed by the inner end 30 ofthe first element 26 and the base 12, a second interior angle formed bythe inner end 32 of the second element 28 and the base 12, and a thirdangle formed by the remainder portions 34, 36 of the two elements 26,28. These three angles may be equivalent or different degrees inmeasurement. In many embodiments, the angles are all less than about 90degrees, and in some embodiments, the angles are all less than about 75degrees. In particular embodiments, the triangular shape approximates anisosceles triangle with the three angles each being about 60 degrees.However, the first and second angles may be less than 60 degrees, sincethe partially toroidal base will provide some arc. For example, thetriangular extension portion 14 illustrated in FIG. 3 has three interiorangles, each measuring about 60 degrees. If the third angle of FIG. 3 is60 degrees, the first and second interior angles would still be lessthan 60 degrees due to the upward arch of the base 12.

The extension portion also may comprise braces. The braces may providesome structural stability and support to the extension portion, and mayprovide some alternative pathways for electricity flow through the coil.For example, the extension portion 14 of the device 11 illustrated inFIG. 1 has first and second elongated braces 38, 40, each brace havingfirst ends 42, 46 and second ends 44, 48. The first end 42 of the firstbrace 38 is coupled adjacent to the inner end 30 of the first elongatedelement 26, and the second end 44 of the first brace 38 is coupled tothe base 12. The first end 46 of the second brace 40 is coupled adjacentto the inner end 32 of the second elongated element 28 and the secondend 48 of the second brace 40 is coupled to the base 12. In thisparticular embodiment, the braces 38, 40 are coupled to the base 12between each inner end 30, 32 of the elongated elements 26, 28. In thisparticular embodiment, the braces 38, 40, elongated elements 26, 28, andbase 12 also define triangular shapes. However, other embodiments mayhave braces coupled to different portions of the elongated elementsand/or base, or may not include such braces at all.

In the embodiment illustrated in FIG. 1, the base includes a pair ofsubstantially parallel, arcuate, elongate, longitudinally-extending,laterally spaced frame members 21 and 23. These have the arcuateconfiguration illustrated in FIG. 3. Extending between andinterconnecting longitudinal frame members 21 and 23 are ten elongate,arcuate transverse frame members 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. As isseen in FIG. 1, members 1-10 are spaced apart along the lengths oflongitudinal frame members 21 and 23 and are coupled at their oppositeends to, and extend generally at right angles to, longitudinal framemembers 21 and 23. Arcuate transverse frame members 1, 2, 3, 4, 5, 6, 7,8, 9, 10 may be spaced apart from each other by any suitable distance,such as from about 1 mm to about 5 cm, depending on the overall lengthof base 12 and the number of arcuate transverse frame members. Thedistance between two adjacent arcuate transverse frame members 1, 2, 3,4, 5, 6, 7, 8, 9, 10 may be the same as or different than the distancebetween two other arcuate transverse frame members 1, 2, 3, 4, 5, 6, 7,8, 9, 10. In particular embodiments, arcuate transverse frame members 1,2, 3, 4, 5, 6, 7, 8, 9, 10 are separated from each other by a distanceof about 1 cm.

However, in alternative embodiments, the longitudinally extendinglaterally spaced frame members, 21 and 23, are not substantiallyparallel along their entire lengths. This non-parallel orientation maybe accomplished by altering the lengths of the transverse elements alongthe base. For example (and without limitation), the transverse elementsnear the first end of the base may be shorter than the transverseelements near the second end of the base.

Extension element 26 includes a pair of elongate, substantiallyparallel, spaced extension frame members 50 and 51. Extension element 28includes a pair of elongate, substantially parallel, spaced extensionframe members 52 and 53. The lower ends of members 51 and 53 are coupledto spaced apart locations on longitudinal frame member 23 and the lowersets of ends of members 50 and 52 are coupled at spaced apart locationsto longitudinal frame member 21. Three spacer members 58, 60, and 62extend between frame members 50, 51, 52, 53 to maintain a selectedspacing therebetween.

Brace 38 includes a pair of elongate, laterally spaced elements 54 and55 which are coupled at their upper ends to frame members 50 and 51, andat their lower ends to longitudinal frame members 21 and 23respectively. Similarly, brace 40 includes a pair elongate, laterallyspaced elements 56 and 57 coupled at their upper sets of ends toextension frame members 52 and 53 and at their lower ends tolongitudinal frame members 21 and 23, respectively.

The embodiment illustrated in FIGS. 1-4 includes a minimal number ofcomponents extending radially of the base to form extension 14. Inalternative embodiments, extension 14 includes a greater number ofradially extending components, such as the embodiment illustrated inFIGS. 8-11, described in more detail below.

As stated above, the device comprises a frame and an electricallyconductive coil. In some embodiments, the frame itself may function asthe coil. However, in other embodiments, the coil comprises a separatestructure as part of the device, and may even include multiple coils.FIG. 2, discussed in more detail below, is an electrical circuit diagramfor one possible coil configuration for the embodiment illustrated inFIG. 1.

In particular embodiments, the coil comprises one or more windings of anelectrically conductive material, such as a metal wire. These windingscomprise electrical transducers. In these embodiments, the windings areassociated with the frame; for example, wire may be run alongside of, bemounted to, or placed inside of the frame, so long as the wire formingthe windings does not contact any electrically conductive portion of theframe. Such a configuration is shown in FIG. 5, which shows a crosssection through the base 12 illustrated in FIG. 1.

In FIG. 5, an exemplary frame element 64 and conducting wire 66 areshown surrounded by an insulating material 68, such as plastic orrubber. If the frame is made of an electrically conductive material, thewire 66 would need to be spaced apart from the frame element 64, and maybe separated from the frame element 64 by a layer of the insulatingmaterial 68. Additionally, a cross section through other parts of thebase 12 or extension portion 14 of the embodiment illustrated in FIG. 1might show plural wires, depending on the placement of windings on theframe. In some embodiments, a winding is associated with an elongatedelement, a brace element, or both. In particular embodiments, a windingis associated with each elongated element and each brace element.

FIG. 2 is a schematic electrical diagram illustrating conducting wiresand current flow in the embodiment illustrated in FIG. 1. In FIG. 2,points labeled A-J and AA-JJ are associated with the base, and pointsQ-V are associated with the extension portion. Points U and V correspondto the electrical inputs for the current produced by the power supply(not shown). Using the circuit diagram of FIG. 2 as a guide, one canunderstand how a coil might be constructed for the embodiment of FIG. 1.For example, the device 11 illustrated by FIG. 1 could comprise a coilhaving ten windings numbered 1-10 extending in the arch width directionof the base along the ten elongate, arcuate transverse frame members1-10. Table 1 summarizes such a placement of windings.

TABLE 1 Winding No. Pathway 1 V-R-H-I-J-JJ-II-HH-Q-U 2 V-R-H-I-II-HH-Q-U3 V-R-H-HH-Q-U 4 V-R-F-G-GG-FF-Q-U 5 V-R-F-FF-Q-U 6 V-T-E-EE-S-U 7V-T-E-D-DD-EE-S-U 8 V-T-C-CC-S-U 9 V-T-G-B-BB-CC-S-U 10V-T-C-B-A-AA-BB-CC-S-U

Alternative embodiments of the device could comprise a coil with more orless than ten windings, however. Furthermore, the windings couldcomprise a single wire or plural wires, such as separate wires for eachwinding. In some embodiments, different windings may have differentnumbers of wires. In some embodiments, the different windings of thecoil are connected in series. However, in alternative embodiments,windings are connected in parallel. Alternatively, the deviceillustrated by FIGS. 1 and 2 could be produced by a coil comprising asingle winding, such as a coil comprising an electrically conductiveframe, so long as the coil comprised an appropriate circuit.

The device coil illustrated by the FIG. 2 circuit diagram is made up oftransducers. However, the device also may comprise other electricalcomponents, such as resistors, inductors, or capacitors to produce anappropriate circuit, such as the circuit illustrated in FIG. 2. Whetherother electrical components are necessary for a particular embodimentwill depend on several factors including, (but not limited to): the typeof generator used; the frequency, amperage, and voltage of the currentpassing through the circuit; the resistance of the transducer(s); andthe timing of activation of the circuit.

The particular embodiment illustrated by FIGS. 1 and 2 has a coilcomprising two major portions: a portion associated with the partiallytoroidal or ovate base 12, and a portion associated with the extensionportion 14. In this embodiment, the length of the portion of the coilcomprising the base is oriented substantially parallel to the width axisof the base by associating the coil with several transverse frameelements 1-10. These transverse strips of the coil correspond tosections 1-10 of the circuit diagram in FIG. 2 (i.e., pathways A-AA,B-BB, C-CC . . . H-HH, I-II, and J-JJ). In such an embodiment, asignificant portion of the current flowing through the base flowsthrough these strips and, therefore, is oriented substantially along thereference z-axis shown in FIG. 1. Additionally, as further illustratedby FIGS. 3 and 4, the coil portions associated with the base arecomplementary and tangential to the surface of the subject's skull. Inparticular embodiments, the total length of the coil associated with thetransverse frame elements 1-10 (i.e., substantially parallel to thewidth axis of the base) exceeds the remaining length of the coilassociated with the base (i.e., the remaining length substantiallyparallel to the length axis of the base). In these embodiments, amajority of the current flowing through the base is orientedsubstantially along the referenced z-axis shown in FIG. 1.

The device also may comprise a cushion placed adjacent to the first sideor underside 19 of the base 12 which faces the subject. A cushion madefrom suitable material, such as cloth, foam, or rubber, may provide anadditional measure of comfort for a subject when the device is used onthe subject. Additionally, as illustrated in FIG. 5 the device may alsocomprise some nonconductive material, such as plastic or rubber, thatencases the frame and coil.

The device also may comprise a shield or screen (not shown, for sake ofclarity) placed around one or more elements of the extension portion 14.This shield or screen can inhibit or block the magnetic fields producedwhen electricity runs through the portions of the coil in extensionportion 14. Since the magnetic fields produced by the extension caninterfere with the magnetic fields produced by the portions of the coilin base 12, screening the magnetic fields produced by extension portion14 can reduce the interference with the magnetic fields produced by base12 and, therefore, increase the strength of the electrical fieldsinduced in a conductive medium by the magnetic fields of base 12. Asjust one, non-limiting example, Example 3 below, and FIGS. 12-13, showthe effects of screening the return paths of extension 14. Any suitablescreen or shield capable of inhibiting magnetic fields may be used,though in some embodiments, a metal is used as a screen, such as mumetal, which is known to efficiently screen magnetic fields. The screenmay be any suitable size or shape, including (but not limited to),sheaths of mu metal surrounding one, some, or all of the elements ofextension 14; a flat disc of metal placed intermittently withinextension 14 that would inhibit the magnetic and electric fieldsproduced by extension 14 from interfering with those produced by base12; or an enclosure substantially enclosing extension 14. This shieldingdiverts the magnetic flux produced by the extension portion to theshielding, thus reducing interference with the fields produced by thebase portion.

An alternative embodiment of the device is illustrated at 11A in FIGS.8-10 placed on a human head 100. Similar to the first embodiment (FIGS.1-4) in many ways this alternative embodiment has a base 12A andextension portion 14A, where base 12A has a first end 22A and second end24A, and a substantially arcuate, semicircular or semi-ovate shape alongits length and width axes. However, in this embodiment, extension 14Aincludes a plurality of radially elongated extension elements 110, 112,114, . . . 158, 160, rather than a minimal number of radially extendingelongated elements 26, 28 (see FIGS. 1, 3 and 4). This embodimentincludes twenty-six radially extending elongated extension elements 110,112, 114, . . . 158, 160, although alternative embodiments may employ adifferent number of such elongated extension elements. As illustrated,the radially extending elongated elements 110, 112, 114, . . . 158, 160are collected into four fan-like groupings 170, 172, 174, 176, andelongated elements 134 and 136 are connected by lateral elements 180 and182.

As illustrated in FIG. 9 elongated elements 110, 112, 114, . . . 158,160 may extend substantially orthogonally from base 12A or, asillustrated by the dotted lines, may be offset from this orthogonalorientation at an angle, θ. The degree of offset (θ) may be up to 60degrees to either side of the base, such as less than about 45 degrees,or less than about 30 degrees. In particular embodiments, the degree ofoffset is about 20 degrees. Either all, some, or none of the elongatedelements may be offset. In some embodiments, alternate elongatedelements are offset. For example, elongated elements 112, 116, 120 . . .156, 160 may be offset 20 degrees, while elongated elements 110, 114,118, . . . 154, 158 may be oriented substantially orthogonally to base12A.

Similar to the extension portion illustrated in FIGS. 1, 3 and 4, theextension illustrated in FIGS. 8-9 may be a unibody element or aconstruction of plural components.

Similar to base 12 illustrated in FIGS. 1, 3 and 4, base 12A illustratedin FIGS. 8-9 includes a pair of substantially parallel, arcuate,elongate, longitudinally-extending, laterally spaced frame members 21Aand 23A. Extending between and interconnecting longitudinal framemembers 21A and 23A are twenty-six elongate, arcuate transverse framemembers 210, 212, 214, . . . 258, 260.

The amount of surface charge, and the influence of that surface chargeon the deeper tissues of the subject's body that are stimulated, dependson the overall lengths and locations of the electrical components whichcontain radial components. In this embodiment, the overall length ofsuch radial elements is reduced and their distances from the subject'sbody are increased, relative to the embodiment shown in FIGS. 1-4. Inother words, the ratio of the total length of the coil extendingradially from the base to the total length of the coil associated withthe base is less than the corresponding ratio in other embodiments, suchas the embodiment illustrated in FIGS. 1-4.

Referring to the extension element shown in FIG. 9, which is exemplaryof the other extension elements, it includes a pair of elongate,substantially parallel spaced elongate extension frame members 310 and312, with each frame member connected to one of laterally spaced framemembers 21A and 23A. The first ends of the extension frame members, suchas 310, are connected to spaced apart locations on frame member 21A,while the first ends of extension frame members, such as 312, areconnected to spaced apart locations on frame member 23A. The second, orouter, ends of the extension frame members, such as 310 and 312, areinterconnected by transverse spacer frame members, such as 314.

In this second embodiment, base 12A includes twenty-six transverseelements 210, 212, 214, . . . 258, 260 (which may be referred to as“strips”), compared to the ten transverse elements 1-10 of the firstembodiment (see FIG. 1). Extension 14A of this second embodimentincludes twenty-six elongated elements 110, 112, 114, . . . 158, 160grouped into four fan-like collections 170, 172, 174, 176. Theseelongated elements 110, 112, 114, . . . 158, 160 are coupled to base 12at locations adjacent certain transverse elements 210, 212, 214, . . .258, 260. For example, as illustrated in FIG. 8, elongated elements 110,112, 114, 116, 118, and 120 are coupled to base 12A adjacent transverseelement 222; elongated elements 122, 124, 126, 128, 130, 132 and 134 arecoupled to base 12A adjacent transverse element 226; elongated elements136, 138, 140, 142, 144, 146, and 148 are coupled to base 12A adjacenttransverse element 244; and elongated elements 150, 152, 154, 156, 158,160 are coupled to base 12A adjacent transverse element 248. Inalternative embodiments, however, each elongated element may be coupledto the base in a different arrangement. Each elongated element may beseparately coupled to the base adjacent a single transverse element, ordifferent numbers of elongated elements may be grouped together andcoupled to the base adjacent certain transverse elements. For example(and without limitation), pairs of elongated elements may be coupled tothe base adjacent every other transverse element, or groups of multipleelongated elements may be coupled to the base adjacent six individualtransverse elements.

The elongated elements 110, 112, 114, . . . 158, 160 within anindividual fan 170, 172, 174, and 176 may be regularly spaced apartfrom, or angularly disposed relative to, each other. For example (andwithout limitation), as shown in FIG. 8, the elongated elements of fans170 and 176 are spaced apart, or angled, from each other by about 8degrees, while the elongated elements of fans 172 and 174 are spacedapart from each other by about 6 degrees.

As in the first embodiment, the longitudinally-extending laterallyspaced frame members, 21A and 23A, may be oriented substantiallyparallel to each other, or may be placed in a non-parallel orientation.

FIG. 11 is a schematic illustration of current flow through the windingsof the embodiment illustrated in FIG. 8, with reference numeralscorrelating these windings to certain structures illustrated in FIGS.8-10. FIG. 11 is not a circuit diagram in the true sense-thisillustration simply shows how a coil for the device may be made fromindividual windings of the coil, with each individual winding comprisinga circuit. For the sake of clarity, only part of the entire device isshown. Additionally, FIG. 11 illustrates only one exemplary,non-limiting pattern of current flow. Other embodiments may exhibit adifferent pattern of current flow due to a different placement ofwindings, and in particular embodiments, the windings are connected inseries and current passing through the strips of the base (i.e., flowingthrough the windings associated with the transverse elements of the basebetween the lateral frame members) flows in the same direction.

As illustrated in FIG. 11, the direction of electrical current flow isthe same in all of the twenty-six strips of the base 12A (illustrated inFIGS. 8-10); flowing in a direction from the lateral frame member 23A tolateral frame member 21A. Generally, current to this portion of the coilarrives at Z, travels down to I₂, and flows through strips J₂-J₁, K₂-K₁,L₂-L₁, and M₂-M₁. Each strip (A₂-A₁, B₂-B₁, . . . M₂-M₁) has a returnpath through an elongated element 110, 112, 114, . . . 158, 160 of oneof the fan-like groupings 170, 172, 174, 176. For example, the returnpath for strip J₂-J₁ may be elongated element 140 (not shown in FIG.11). The current flow to I₂ then flows through strip H₂-H₁ and to I₁.From here, the current flows up the extension to W. then to X (the lineW-X representing the junction of two elongated elements, 148 and 150),then to G₂, then through strips F₂-F₁, E₂-E₁, D₂-D₁, C₂-C ₁, B₂-B₁,A₂-A₁, and returns to G₂. Each of strips F₂-F₁, E₂-E₁, D₂-D₁, C₂-C₁,B₂-B₁, A₂-A₁, has a return path through an elongated element of fan-likecollection 176 composed of elongated elements 150-160. For example, thereturn path for strip F₂-F₁, is shown by the G₁-U-V-G₂ pathcorresponding to elongated element 260 in FIGS. 8-9. Other strips (e.g.,E2-E1, D2-D1, C2-C1) have return paths through other elongated elements(not shown in FIG. 11) anchored at the G2-G1 strip (i.e., elongatedelements that are part of fan-like collection 176, shown in FIGS. 8-9).After flowing through the strips and return paths, the current flows toG₁, then to W (through another winding, against the illustrated arrow),on to X, back to I₂, then I₁, and returns to the other end of the device(not shown) via Y.

The return path of current flow is in the opposite direction of thestrips, although these return paths of the coil associated with base 12A(i.e., along transverse elements 210, 212, 214, . . . 258, 260) arephysically spaced apart from base 12A by associating the return pathswith transverse spacer frame members, such as 314 in FIG. 9, ofextension 14A. The physical distance between the strips and return pathsmay be any suitable distance, such as about 1 cm, 5 cm, 10 cm, or more.In certain embodiments, the return paths are separated from the stripsby a distance of at least about 5 cm; for example, as illustrated inFIG. 9, the physical distance between the portion of the coil in base12A at transverse element 210 and the return path of the coil alongtransverse spacer frame member 314 is at least about 5 cm.

Similar to the first embodiment illustrated in FIGS. 1-4, this secondembodiment may include a frame made of flexible or malleable material,for example, to conform base 12A to the shape of a subject's skull, andmay include a cushion placed adjacent to the underside of base 12A forproviding an additional measure of comfort for a subject. Additionally,the device may contain a shield or screen that inhibits or blocks themagnetic fields of extension 14A.

Thus, as in the embodiment illustrated in FIGS. 14 and 8-10, thecomponents of base 12A and extension 14A may form an electrical coil,either by using frame elements that are electrical transducers orassociating a transducer (such as a wire) with the frame (e.g., asillustrated in FIG. 5 and discussed above). The extension portion 14Aprovides a return path for the electricity flowing through the base 12A.As in the first embodiment (FIGS. 1-4), extension portion 14A of thissecond embodiment places electrical currents flowing through the returnpaths away from the subject, to reduce their electrical effect on thebody tissues of the subject. In embodiments where the coil comprises oneor more windings of electrically conductive material (e.g., metal bandsor wires), the wire and frame elements may demonstrate the configurationillustrated in FIG. 5.

The device described above can be used in a variety of ways and on anypart of a subject's body. Any conductive tissue, including (but notlimited to) nervous tissue and muscle tissue, may be stimulated by thedevice. The device creates a time-varying magnetic field capable ofpenetrating the body of a subject that, in turn, can induce an electricfield within a conductive tissue of the body. These induced electricfields may stimulate such conductive tissues. For example, the device iscapable of depolarizing a neuron within the body of the subject,including neuron comprising the central nervous system, such as thosefound in the brain.

The device may be used on any appropriate subject. For example, thedevice may be used on humans for treating or studying certainphysiological conditions, such as neurophysiological or cardiovascularconditions, or for studying the physiology of the body. The device alsomay be used in similar ways on other types of animals, includingmammals, such as canines, felines, rodents, or primates.

Since magnetic stimulation can alter blood flow, the device may be usedfor studying or treating cardiovascular conditions in various tissues ofa subject's body. For example, the device illustrated in FIG. 1 may beused in TMS applications to monitor or regulate blood flow through thebrain of a subject, such as a subject at risk for suffering a stroke.Additionally, the device may be used to monitor or to regulate bloodflow during reperfusion following a cardiovascular event, such as strokeor other blockage of a blood vessel. The device may be used for studyingtreating cardiovascular conditions associated with parts, tissues, ororgans of the body other than the brain, such as the heart, lungs,kidneys, liver, and spinal cord.

This device may be used to study or treat a neurophysiological conditionassociated with the deep regions of the brain. A “neurophysiologicalcondition” may be a pathological neurophysiological condition or aneurophysiological disorder, such as (but not limited to): clinicaldepression, non-clinical depression, dysthemia, bipolar disorder, drugaddiction, substance abuse, anxiety disorder, obsessive compulsivedisorder, or Parkinson's disease. The device also is useful for treatingaddiction, such as drug addiction, or other substance abuse, such asalcoholism.

The deep region of the brain includes the nucleus accumbens, and mayinclude other structures such as the ventral tegmentum; the amigdala;and the medial prefrontal and cingulate cortexes. The prefrontal andcingulate cortexes are connected to the nucleus accumbens by denseneuronal fibers, and these fibers are known to play an importantneurophysiological role in substance abuse and drug addiction.Therefore, stimulating these dense neuronal fibers is one way to use thedevice to treat such neurophysiological conditions.

The focus of magnetic field generated by the device coil may be alteredby changing the base. For example, as the width of the base is narrowed,the magnetic field will narrow, thus stimulating a narrower area oftissue. Additionally, narrowing the width of the base will decrease thedepth of the field produced by the coil. Therefore a sufficientlyfocused coil can stimulate selected regions of the body. For example,the coil embodied in FIGS. 1-5, and placed accordingly, is capable ofstimulating the deep regions of the brain and the coronal sectionunderneath the base, but would not stimulate the frontal or occipitallobes of the brain. However, if the coil was placed at a differentportion of a subject's skull (e.g., at the base of the skull, wrappingbehind the subject's head) then a different part of the brain might bestimulated (e.g., the occipital lobe).

One embodiment for using the device comprises identifying a subjectsuffering, or at risk of suffering, a neurophysiological condition;providing an electrically conductive coil as described above (i.e.,having a partially toroidal or ovate base with a concave first side tobe directed toward a body part of the subject); placing the coilexternal to the subject's skull; electrically connecting a power supplyto the coil; and activating the coil to stimulate the deep region of thesubject's brain.

The device also may be used for treating a neurophysiological conditionby identifying a subject suffering a neurophysiological condition andproviding an electrically conductive coil (as described above). The coilis placed external to the subject's skull and activated to stimulate thedeep region of the subject's brain. In particular embodiments, the coilhas a partially toroidal or ovate base portion with a concave first sideto be directed toward a body part of a subject and has an extensionportion projecting outwardly from a second side opposite the first side.In alternative embodiments, the coil has a base portion and an extensionportion, the extension portion comprising a radially elongated extensionelement;

Another embodiment comprises identifying a subject; providing anelectrically conductive coil as described above; placing the coilexternal to the subject's skull; electrically connecting a power supplyto the coil; activating the coil to stimulate the deep region of thesubject's brain; and localizing and characterizing brain function. Forexample, the coil could be used in combination with brain imaging, suchas magnetic resonance imaging (MRI) or positron emission tomography(PET), to study the effect of deep brain stimulation on other regions ofthe brain. Additionally, the subject may be directed to carry out sometask, including (but not limited to) speaking, reading, writing, orsleeping. For example, the subject can be directed to move a specificbody part, such as an arm or leg, in order to study the relevantneuronal circuits in the brain. As another example, the subject can bedirected to look at different intensities of light, or different shapes,in order to study the neuronal circuits of the brain associated withvision. Additionally, the subject can be instructed to perform somemathematical task to study higher brain functions. As another example,the coil may be used in conjunction with brain imaging to study theeffects of personal spiritual practices, such as yoga, meditation, orprayer.

Yet another embodiment comprises non-invasively stimulating a subject'sbrain. “Non-invasively” means the subject's brain, including the deepregions of the brain, can be stimulated with the device coil placedexternally of the subject's skull. In other words, the subject's brain,including the deep regions of the brain, can be stimulated withoutplacing the coil in an orifice of the subject's head, such as the mouth,or introducing the coil into the subject's skull via a surgicalprocedure.

In some embodiments, a train of electromagnetic pulses is administeredto the subject. Individual pulses measuring from about 50 to about 2000microseconds in duration are produced by the coil, and the pulse lengthmay be altered according to various factors including (but not limitedto) the tissue stimulated, the particular coil construction or shape, orthe physiological condition of the subject. A duration of about 1000microseconds is capable of stimulating nervous tissue.

The train may comprise an appropriate number of individual pulsesadministered over a certain period of time. In some embodiments, a trainof about 1 to about 100 pulses is administered. Specific embodimentsemploy a number of pulses within a specific range, such as less than100, less than 75, less than 25, or 25 to 50, 10 to 75, 5 to 100, 5 to25, 25 to 75, or 75 to 100. Alternative embodiments employ a specificnumber of pulses, such as 75, 60, 50, 40, 25, 10, 5, 1, or any of 1 to100.

The pulses may vary in frequency as well as number. Certain embodimentsuse a frequency range of from about 1 to about 100 Hz, while otherembodiments employ pulses of from about 5 to about 60 Hz, or moreparticularly, from about 20 to about 30 Hz. Additionally, pulses withina train of pulses may be administered at different frequencies.

In some embodiments, two or more stimulator channels may be connected tothe coil, which can create close interval pulses. In such embodiments,the interpulse interval may be one millisecond or longer in duraction.The use of multiple stimulator channels may allow differentialstimulation of the brain by using different intensities or frequenciesfor stimulating different regions of the brain.

The train of pulses may be administered during a certain period of time,such as from about 1 to about 120 seconds. Particular embodimentsinvolve administering the train of electromagnetic pulses during aperiod of time of from about 2 to about 60 seconds, or moreparticularly, a period of time of from about 20 to about 30 seconds. Thedelay between pulses may vary, but certain embodiments use delays ofsimilar duration.

Embodiments of this method of treating or studying a particularcondition of a subject also may involve administering a train (or pluraltrains) of electromagnetic pulses during a session. The entire treatmentor study regimen may be conducted over an indefinite period of time, ormay involve a certain number of sessions, such as from about 1 to about30 sessions, over a certain period of time, such as 1 to 8 weeks, 2 to 7weeks, 3 to 6 weeks, 4 to 5 weeks, less than one week, or longer than 8weeks. Alternative embodiments employ a single session.

A plurality of trains may have an intertrain interval of time.Particular embodiments have an intertrain interval measuring from about5 to about 240 seconds, from about 20 to about 180 seconds, or fromabout 60 to about 120 seconds. As just one non-limiting example, aplurality of electromagnetic pulse trains may be administered in thefollowing manner: a train of 50 pulses over 60 seconds; an intertraininterval of 40 seconds; a train of 20 pulses over 120 seconds; anintertrain interval of 30 seconds; a train of 30 pulses over 60 seconds;an intertrain interval of 10 seconds; a train of 30 pulses over 90seconds.

If the subject is suffering a specific condition, such as aneurophysiological condition, then the sessions may last until clinicalimprovement occurs. For example, the subject might be a human sufferingclinical depression and the treatment may last until the subject nolonger tests for clinical depression. As another example, the subjectmight be a human suffering drug addiction, and the treatment might lastfor a certain number of sessions until the person can manage his or hercravings for the drug.

The number of pulses, train length, and intertrain interval may bevaried according to various factors including (but not limited to): thephysiological condition of the subject; the characteristics of thesubject; the condition being treated or studied; the construction of thecoil; the type of generator or power supply used to generate theelectromagnetic pulses; or the number of generators or power suppliesused.

EXAMPLES

The following examples are provided to illustrate particular features ofthe present invention. The scope of the present invention should not belimited to the features illustrated by these examples.

Example 1 Considerations for a Transcranial Magnetic Stimulator Coil

A coil was designed for deep brain stimulation in accordance with thepresent invention.

In order to develop a TMS coil for stimulation of deep brain regions,several factors were considered. For TMS stimulation, a brief, butstrong current should be passed through a coil of wire, generating atime-varying magnetic field (B). An electric field (E) is generated atevery point within the magnetic field (B), having a directionperpendicular to the magnetic field (B) and proportional to thetime-rate of change of the vector potential (A(r)). The electric field(E) induced by the magnetic field (B) induces action potential inexcitable neuronal cells, which in turn results in activation ofneuronal circuits if an electric field (E) above certain threshold iscreated. The resulting induced electric currents are proportional to theelectric field (E) amplitude.

The vector potential A(r) in position r is related to the current I in awire (I) by the expression:

$\begin{matrix}{{A(r)} = {\frac{\mu_{0}I}{4\;\pi}{\int\frac{\mathbb{d}l^{\prime}}{{r - r^{\prime}}}}}} & (1)\end{matrix}$Where μ₀=4π* 10⁻⁷ Tm/A is the permeability of free space, T is tesla, mis meters, and A is ampere. The integral of dl′ is over the wire path,where dl′ is an element of wire, and r′ is a vector indicating theposition of the wire element.

The magnetic and electric fields resulting from the current in the wire(B_(A) and E_(A) respectively) are related to the vector potentiB _(A) =∇×A(r)  (2)where ∇× is curl, and:

$\begin{matrix}{E_{A} = {- \frac{\partial{A(r)}}{\partial t}}} & (3)\end{matrix}$where t is time.

Under these equations, the current (I) is the only variable changingover time. Hence, the electric field E_(A) can be described as:

$\begin{matrix}{{E_{A} = {{\frac{\mu_{0}}{4\;\pi}\frac{\partial I}{\partial t}{\int\frac{\mathbb{d}l^{\prime}}{{r - r^{\prime}}}}} = {C{\int\frac{\mathbb{d}l^{\prime}}{{r - r^{\prime}}}}}}}{{with}\mspace{20mu} C} = \frac{\mu_{0}{\partial I}}{4\;\pi{\partial t}}} & (4)\end{matrix}$

Since brain tissue has conducting properties, while the air and skullare almost complete insulators, the vector potential will induceaccumulation of electric charge at the brain surface. This surfacecharge (E_(Φ)) is another source for the electric field (E) and can beexpressed as:E _(Φ)=−∇Φwhere ∇ is divergence and Φ is the scalar potential produced by thesurface electrostatic charge.

The total electric field in the brain tissue (E) is the vectorial sum ofthese two fields:E=E _(A) +E _(Φ)  (6)The surface electrostatic field (E_(Φ)) generally opposes the inducedfield (E_(A)). Consequently, as the strength of the electrostatic field(E_(Φ)) increases, the strength of the total field (E) decreases.However, the amount of surface charge produced (and, hence, themagnitude of E_(Φ)) correlates to coil orientation.

If an electric field (E) is generated by a coil placed external to theskull, certain parts of that field will lie parallel or tangential tothe skull of the subject, while other parts of the electric field (E)will lie perpendicular to the skull of the subject. The perpendicularcomponents will induce a surface charge (E_(Φ)) at the surface of thebrain. As the magnitude of surface charge (E_(Φ)) increases, themagnitudes of the perpendicular parts of the electric field (E)decrease. A sufficiently large surface charge (E_(Φ)) would completelycancel out the perpendicular parts of the field, so only the parallelparts of the total field (E) would remain. See, Tofts, P. S., Phys. Med.Biol., 35:1119-28 (1990); Tofts, P. S. and Branston, N. M.,Electroencephal. Clin. Neurophysiol., 81:238-9 (1991). This cancellationof the perpendicular parts of the field is a direct consequence ofMaxwell equations with the appropriate boundary conditions.

If a surface charge (E_(Φ)) does exist, the parallel components of thetotal electric field (E) generated by a coil placed external to theskull diminish in strength within the tissue. For example, it has beenreported that, for a simple model of the brain as a flat homogeneousvolume conductor, the surface field can reduce the strength of the totalfield resulting from a circular coil placed perpendicular to the tissue(i.e., the coil is placed on its edge against the tissue) by 42% along aline perpendicular to the surface and passing through the center of thecoil. See, Roth, B. J., et al., Muscle Nerve, 13:734-41 (1990); Tofis,P. S. and Branston, N. M., Electroencephal. Clin. Neurophysiol.,81:238-9 (1991).

Thus, as the perpendicular field produced by any coil increases, moresurface charge is induced, thus diminishing the total electric field inthe tissue. Therefore, coils capable of stimulating deep brain regionsproduce significant field strength in directions parallel to the surfacewith reduced perpendicular components of the induced field. Theembodiment illustrated in FIGS. 1-5 accomplishes these objectives byemploying a substantially toroidal or ovate shaped base-where the coilportions along the length and width axes of the base lie parallel to theskull of the human subject.

Example 2 Comparison with Known Coil Designs

A coil produced according to the present invention and under theconsiderations of Example #1 is compared to available known coils withrespect to their suitability for activating deep brain regions.

Known coils can stimulate cortical or peripheral nerves, but theelectric fields induced by such known coils decrease rapidly as distancefrom the coil increases. For example, the electric field induced by a9.2 cm diameter circular known coil was measured using a volumeconductor filled with saline. The coil was placed parallel to thesurface of the volume (i.e., the coil was placed as flat as possibleagainst the volume, rather than placing it edge-on against the volume).See, Maccabee, P. J., et al., Electroencephal. Clin. Neurophysiol.,76:131-41 (1990). The field induced at a distance of 2.5 cm from thecoil was less than 60% of the field induced at a distance of 0.5 cm fromthe coil. Moreover, the field induced at a distance of 4.0 cm from thecoil was less than 40% of the field at induced at a distance of 0.5 cmfrom the coil. Id.

For a FIG. 8 coil, the field strength decreases more rapidly. Forexample, a FIG. 8 coil having two rings, each 4.8 cm in diameter,oriented parallel to (i.e., placed flat against) the conductor surface,induced a field at 2.5 cm from the coil center that was about 30% of thefield at 0.5 cm from coil center. Id. Similar results were obtained inmathematical calculations of the induced electric field. See Cohen, L.G., et al., Electroencephal. Clin. Neurophysiol., 75:350-7 (1990). Whilethe use of an array of circular or FIG. 8 coils placed parallel to theskull can, in some cases, improve the focality of the field at thecortex, multiple coils will not counteract this rate of decrease infield strength with increasing distance from the coil. See Ruhonen, J.,and Ilmoniemi, R. J., Med. Biol. Eng. Comput., 38:297-301 (1998).

Placing a circular coil perpendicular to a skull surface (i.e., standingthe coil on edge against the skull) may allow increased percentagestrength of the field at a depth, relative to the field strength at thesurface, compared to placing the coil parallel to (i.e., flat against)the skull surface. Tofts, P. S.,Phys. Med. Biol., 35:1119-28 (1990);Tofts, P. S. and Branston, N. M., Electroencephal. Clin. Neurophysiol.,81:238-9 (1991). However, the absolute magnitude of the field, both atthe surface and in deep regions of the brain, is reduced due toaccumulation of charge at the surface (as described in Example 1), sincea coil placed perpendicular to the skull surface will generate a fieldlargely perpendicular to the skull surface, thus generating a greatersurface charge (E_(Φ)).

Another coil, termed a “slinky coil” is composed of several windings inintermediate orientation between FIG. 8 coil and a circular coil. See,Ren, C., et al., IEEE Trans. Biomed. Engineering, 42:918-25 (1995);Zimmermann, K. P., and Simpson, R. K. Electroencephal. Clin.Neurophysiol., 101:145-52 (1996). If placed on the surface of asubject's skull, a slinky coil may achieve a greater field magnitude andbetter focality at the brain surface near the coil center, but—like thecircular and FIG. 8 coils—a slinky coil generally does not induce anelectric field at a distance sufficient to stimulate the deep regions ofthe brain.

The coil of the present invention was compared to other coils usingcomputer simulations of electric field distribution in a sphericalconductor. The computer simulations were conducted using the Mathematicaprogram (Wolfram, 1999). In these simulations, a subject's skull wasmodeled as a spherical homogeneous volume conductor with radius of 7 cm.The induced electrical field (E_(A)) and electrostatic surface field(E_(Φ)), at specific points inside the spherical volume, were computedfor several coil configurations using the method presented by Eaton.Eaton, H., Med. Biol. Engineering and Computing, 30:433-40 (1992).

The simulations revealed that, in coil configurations havingperpendicular current components, accumulating surface charge diminishestotal field strength. The presence of a surface electrostatic field notonly reduces the total field strength at any point, but also leads tosignificant reduction in the relative strength of the total field(relative to total field strength at the surface) with increasingdistance.

FIG. 6 is a plot of field strengths E (measured in V/m) for thez-components of the induced electric field (rectangles) and totalelectric field (triangles) of a one turn circular coil with diameter ofD=5.5 cm placed perpendicular to the head. The z-components of theinduced and total electric fields are the components lying in adirection tangential to the coil at its center. The electric field wasmeasured in Volt/meter, and the rate of current change in all thecalculations was taken as ∂I/∂t=1000 Amper/100 microseconds. Thesecomponents are plotted as a function of distance from the coil along acentral line perpendicular to the surface that passes through coilcenter.

For comparison purposes, the FIG. 6 graph also depicts the z-componentof the total field strength generated by a single winding (e.g., windingnumber 5) of the coil illustrated in FIGS. 1 and 2, termed a “onestrip”coil. As above, the z-component refers to the electric field componentslying in a direction tangential to the strip at its center. The portionsof the onestrip coil near the surface of the skull lie substantiallyparallel to the surface of the skull and, thus, little or no surfacecharge is induced. Thus, the total field strength largely represents thestrength of the induced field.

FIG. 7 is a graph comparing the field strength of the onestrip coil withthe entire coil illustrated by FIGS. 1 and 2 (i.e., all ten windings),termed the “Hesedcoil,” where each winding has one wire. As shown bythis graph, this version of the Hesedcoil can produce an inducedelectric field of approximately 60 V/m at a distance of 6 cm from thecoil, thus surpassing the threshold activation potential for neurons atthese depths in the brain. Embodiments of the Hesedcoil having morewires, in several or all of the windings, may produce stronger electricfields at such distances.

Example 3 Analysis of a Second Embodiment

Similar to Examples 1 and 2, a second embodiment of the coil,illustrated in FIGS. 8-10, was analyzed for its ability to stimulatedeep regions of the brain.

Theoretical computerized calculations were preformed using theMathematica program as described above, assuming a conductive spherewith a radius of 7 cm. Additionally, measurements of a model of thehuman skull (average diameters: 15 cm×18 cm×23 cm), constructed fromglass and filled with a saline solution, were preformed using a pickupprobe for measuring the electric field in the Z direction in differentspots within the model skull. For all measurements and calculations, therate of current change was taken as 10000 Amper/100 microsec (which isapproximately the maximal power output of standard, commerciallyavailable electrical stimulators). The field is described in Volt/meter.

According to the theoretical calculations, the maximal electric fieldwithin the brain was found to be adjacent to the middle of transverseelement 260, as shown in FIG. 8. This theoretical calculation wasconfirmed by measurements of the model brain. Since this area representsthe maximal electric field, the percentage of field strength at certaindepths within the brain was measured relative to this location. Usingthe model brain, a pickup probe was moved along a line between thecenters of transverse elements 260 and 210, and similar measurementswere taken using the theoretical model.

As shown in FIGS. 11 and 12, the actual electric field induced in themodel brain (designated as the “phantom brain” in FIGS. 11 and 12 andrepresented by open circle notations on the charts) was slightly lowercompared to the theoretical calculations (represented by filled circlenotations on the charts). FIG. 11 is a graph showing actual fieldstrength, while FIG. 12 shows field strength expressed as a percentageof the maximal field in the brain cortex. The maximal field in the braincortex was measured at 1 cm from transverse element 260, which isidentified as “strip 26” in FIG. 12.

The very slight discrepencies between the theoretically expected fieldstrengths at certain distances from the coil and the actual measuredfield strengths may have resulted from the fact that the actual coilused did not have a completely flexible frame and, therefore, not all oftransverse elements 210, 212, 214, . . . 258, 260 would have beenpositioned strictly parallel to the model skull surface. Additionally,the extension portion of the device used differed from the embodimentillustrated in FIGS. 8-10 by having narrower separations betweenadjacent elongated elements 110, 112, 114, . . . 158, 160.

Theoretical calculations of the effect of screening the return paths ofthe extension portion with pieces of metal were also performed (thoughthese measurements were not made with the existing model). As shown inFIGS. 11-12, placing a metal screen around the return paths (i.e.,around some or all of the frame elements making up the extensionportion) can contain the magnetic fields induced by these portions ofthe coil and, therefore, reduce interference with the electric fieldinduced by the base portion of the coil. Furthermore, these calculationsshow that such screening would not only increase the total field inducedanywhere in the brain, but also increase the strength of the field atcertain depths relative to the surface field strength in the cortex ofthe brain.

While the present invention is described in connection with at least twoembodiments, the scope of the present invention is not intended to belimited to any particular embodiment. Instead, the descriptions andexamples disclosed are intended to cover all alternatives,modifications, and equivalents that may be included within the spiritand scope of the invention as defined by the claims.

1. A magnetic stimulator for placing externally of a body part of asubject and operable to induce currents within the body, comprising: anelectrically conductive coil, where the coil comprises a base portionand an extension portion, the extension portion comprising pluralextension elements projecting outwardly from the base portion, whereinthe base portion comprises multiple stimulating elements and wherein theextension portion comprises multiple return elements for return pathsfor current in the stimulating elements, the return elements beingspaced from the stimulating elements so that the electrical effect ofthe return path current on the body part is reduced.
 2. The magneticstimulator according to claim 1, further comprising a frame.
 3. Themagnetic stimulator according to claim 2 where the coil comprises awinding associated with the frame.
 4. The magnetic stimulator accordingto claim 1 where the base portion has a length axis and a width axis,the coil in the base portion comprising elements spaced apart andtransverse to the length axis such that the flow current in theseelements is in substantially the same direction.
 5. The magneticstimulator according to claim 4 where the base portion is a partiallytoroidal or ovate base.
 6. The magnetic stimulator according to claim 4where the base portion comprises plural laterally spaced frame membersextending along the length axis.
 7. The magnetic stimulator according toclaim 6 where at least two of the laterally spaced frame members are ina substantially non-parallel orientation.
 8. The magnetic stimulatoraccording to claim 1 where at least two extension elements are coupledto the base portion adjacent each other.
 9. The magnetic stimulatoraccording to claim 8 where the extension elements are angularly disposedrelative to each other.
 10. The magnetic stimulator according to claim 1where the plural extension elements comprise at least two groups ofplural extension elements, where the extension elements of the samegroup are coupled to the base portion adjacent each other.
 11. Themagnetic stimulator according to claim 1 where an extension elementcomprises a pair of substantially parallel spaced elongate extensionframe members, each extension frame member having an inner end and anouter end, the inner ends of the extension frame members coupled to thebase portion, the outer ends of the extension frame membersinterconnected by a transverse spacer frame member.
 12. The magneticstimulator according to claim 1, further comprising a shield at leastpartially enclosing the extension portion.
 13. The magnetic stimulatoraccording to claim 1, further comprising a power supply electricallyconnected to the coil.
 14. The magnetic stimulator according to claim 1where the base has a concave first side configured to be complementaryto the cranium of a subject.
 15. The magnetic stimulator according toclaim 1 where the coil comprises means for inducing an electric fieldwithin the deep region of the brain.
 16. The magnetic stimulator ofclaim 1, wherein the body part is a skull.
 17. The magnetic stimulatorof claim 1, wherein the extension portion is configured to placeelectrical currents flowing through return paths away from the region ofthe body part having the induced currents.
 18. The magnetic stimulatorof claim 1, wherein the base portion comprises plurallongitudinally-extending laterally spaced frame members.
 19. Themagnetic stimulator of claim 1, wherein a majority of the currentflowing through the base portion is oriented substantially in a singledirection.
 20. A method of treating a neurophysiological condition,comprising: identifying a subject suffering a neurophysiologicalcondition; placing a magnetic stimulator external to the subject'sskull; and activating the coil to stimulate the deep region of thesubject's brain, the magnetic stimulator comprising a base with a firstside to be directed toward a body part of a subject, the base comprisingmultiple substantially parallel stimulating elements configured toconduct electrical current in substantially a single direction ofcurrent flow, thereby inducing electrical fields within the body part,and an extension portion projecting from a second side of the base andcomprising multiple respective return elements for return paths for thecurrent in the stimulating elements, the return elements being spacedfrom the stimulating elements so that the electrical effect of thereturn path current on the body part is reduced.
 21. The methodaccording to claim 20 where the neurophysiological condition is clinicaldepression, non-clinical depression, dysthymia, bipolar disorder, drugaddiction, substance abuse, anxiety disorder, obsessive compulsivedisorder, or Parkinson's disease.
 22. A magnetic stimulator for placingexternally of a body part of a subject and operable to induce currentswithin the body, comprising: a base with a first side to be directedtoward a body part of a subject, the base comprising multiplesubstantially parallel stimulating elements configuTed to conductelectrical current in substantially a single direction of current flow,thereby inducing electrical fields within the body part; and anextension portion projecting from a second side of the base andcomprising multiple respective return elements for return paths for thecurrent in the stimulating elements, the return elements being spacedfrom the stimulating elements so that the electrical effect of thereturn path current on the body part is reduced.
 23. The magneticstimulator of claim 22, wherein the stimulating elements arecomplementary in shape and tangential to the surface of the body partwhen the magnetic stimulator is placed on the body part.
 24. Themagnetic stimulator of claim 22, wherein a majority of the currentflowing through the base is oriented substantially in the singledirection.
 25. The magnetic stimulator of claim 22, wherein therespective return elements comprise current pathways configured to carrythe current in a direction substantially opposite the current in thestimulating elements.
 26. The magnetic stimulator of claim 22, whereinat least some of the respective return elements in the extension portionare spaced from their associated stimulating elements in the base by atleast 5 cm.
 27. The magnetic stimulator of claim 22, further comprisinga shield placed around at least a portion of the extension portion, theshield being capable of inhibiting magnetic fields produced in theextension portion.
 28. The magnetic stimulator of claim 22, where thebase and the extension portion are part of one or more electricallyconductive coils comprising one or more windings.
 29. The magneticstimulator of claim 22, where the extension portion is positionedoff-center relative to the base.
 30. The magnetic stimulator of claim22, wherein the base is flexible or malleable.
 31. The magneticstimulator of claim 22, wherein the stimulating elements of the base arespaced apart from one another.
 32. The magnetic stimulator of claim 22,wherein the base comprises substantially parallel, elongated framemembers, and wherein the stimulating elements extend transverselybetween the frame members.
 33. The magnetic stimulator of claim 22,wherein the extension portion is triangular and comprises at least twoelongated extensions elements that extend away from the base andconverge toward each other.
 34. The magnetic stimulator of claim 22,wherein the extension portion comprises one or more extension elementsprojecting radially outwardly from the base.
 35. The magnetic stimulatorof claim 34, where an extension element comprises a pair ofsubstantially parallel spaced elongate extension members, each extensionmember having an inner end and an outer end, the inner ends of theextension members coupled to the base, the outer ends of the extensionmembers interconnected by a transverse member.
 36. A method of treatingor studying a cardiovascular condition, comprising: identifying asubject at risk of suffering a cardiovascular condition; placing themagnetic stimulator of claim 22 external to the subject's body; andactivating the coil to stimulate the subject.
 37. The method accordingto claim 36 where the cardiovascular condition comprises acardiovascular event.
 38. The method according to claim 37 where thecardiovascular event is a stroke.
 39. A magnetic stimulator forplacement externally of a body part of a subject and operable to inducecurrents within the body, the magnetic stimulator comprising: an arcuatebase having an inner face and an outer face, wherein the base is shapedto conform to a body part on which it is to be externally placed, thebase providing a plurality of stimulating current pathways for inducingthe currents within the body, wherein the stimulating current pathwaysconduct current substantially in a single direction within the base toavoid return current pathways that flow in a direction opposite to thesingle direction and that would oppose or interfere with magnetic fieldswithin the body produced by the stimulating current pathways; and anextension portion extending away from the base that provides the returncurrent pathways, wherein the base comprises first and second spacedlongitudinal sides and the stimulating current pathways extendtransversely of the base between the first and second spacedlongitudinal sides, and wherein current flows through the first andsecond longitudinal sides, the stimulating current pathways, and theextension portion.
 40. A magnetic stimulator for placement externally ofa body part of a subject and operable to induce currents within thebody, the magnetic stimulator comprising: an arcuate base having aninner face and an outer face, wherein the base is shaped to conform to abody part on which it is to be externally placed, the base providing aplurality of stimulating current pathways for inducing the currentswithin the body, wherein the stimulating current pathways conductcurrent substantially in a single direction within the base to avoidreturn current pathways that flow in a direction opposite to the singledirection and that would oppose or interfere with magnetic fields withinthe body produced by the stimulating current pathways; and an extensionportion extending away from the base that provides the return currentpathways, wherein the base comprises a pair of elongated members betweenwhich extend a plurality of the stimulating current pathways, andwherein the extension portion comprises one or more conductive elementsthat form a loop extending outwardly from the plane of the base.
 41. Amagnetic stimulator for placement externally of a body part of a subjectand operable to induce currents within the body, the magnetic stimulatorcomprising: an arcuate base having an inner face and an outer face,wherein the base is shaped to conform to a body part on which it is tobe externally placed, the base providing a plurality of stimulatingcurrent pathways for inducing the currents within the body, wherein thestimulating current pathways conduct current substantially in a singledirection within the base to avoid return current pathways that flow ina direction opposite to the single direction and that would oppose orinterfere with magnetic fields within the body produced by thestimulating current pathways; and an extension portion extending awayfrom the base that provides the return current pathways, wherein theextension portion comprises a plurality of extension elements projectingoutwardly from the base.
 42. The magnetic stimulator of claim 41,wherein the stimulating current pathways are substantially parallel toone another and tangential to the external surface of the body part onwhich the magnetic stimulator is to be placed.
 43. The magneticstimulator of claim 41, wherein the stimulating current pathways arespaced apart from one another.
 44. The magnetic stimulator of claim 41,wherein the base is flexible or malleable.
 45. The magnetic stimulatorof claim 41, wherein the extension portion is triangular and comprisesat least two elongated extensions elements that extend away from thebase and converge toward each other.
 46. The magnetic stimulator ofclaim 41, wherein the extension elements project from the base.
 47. Themagnetic stimulator of claim 41, wherein the extension elements comprisepairs of substantially parallel spaced elongate members interconnectedat their outward ends by transverse members.
 48. A magnetic stimulatorfor placement externally of a body part of a subject and operable toinduce currents within the body, the magnetic stimulator comprising: anarcuate base having an inner face and an outer face, wherein the base isshaped to conform to a body part on which it is to be externally placed,the base providing a plurality of stimulating current pathways forinducing the currents within the body, wherein the stimulating currentpathways conduct current substantially in a single direction within thebase to avoid return current pathways that flow in a direction oppositeto the single direction and that would oppose or interfere with magneticfields within the body produced by the stimulating current pathways; anextension portion extending away from the base that provides the returncurrent pathways; and a shield positioned between the return pathwaysand the stimulating current pathways, the shield being configured toinhibit magnetic fields produced by the return pathways.
 49. A method ofstudying or treating a neurophysiological condition, comprising:identifying a subject suffering a neurophysiological condition; placinga magnetic stimulator external to the subject's skull; and activatingthe magnetic stimulator to stimulate the deep region of the subject'sbrain, the magnetic stimulator comprising, an arcuate base having aninner face and an outer face, wherein the base is shaped to conform to abody part on which it is to be externally placed, the base providing aplurality of stimulating current pathways for inducing the currentswithin the body, wherein the stimulating current pathways conductcurrent substantially in a single direction within the base to avoidreturn current pathways that flow in a direction opposite to the singledirection and that would oppose or interfere with magnetic fields withinthe body produced by the stimulating current pathways; and an extensionportion extending away from the base that provides the return currentpathways.
 50. The method according to claim 49 where theneurophysiological condition is clinical depression, non-clinicaldepression, dysthymia, bipolar disorder, drug addiction, substanceabuse, anxiety disorder, obsessive compulsive disorder, or Parkinson'sdisease.
 51. A method of studying or treating a cardiovascularcondition, comprising: identifying a subject at risk of suffering acardiovascular condition; placing the magnetic stimulator of claim 41external to the subject's body; and activating the coil to stimulate thesubject.
 52. The method according to claim 51 where the cardiovascularcondition is a stroke.
 53. A magnetic stimulator for non-invasivelyinducing electrical fields in a body part of a subject, comprising:means for producing stimulating currents that are complementary to anexternal surface of the body part and oriented in substantially a singledirection; and means for conducting return path currents associated withthe stimulating currents away from the external surface of the body partso that the electrical effects of the return path currents on the bodypart are reduced.
 54. The magnetic stimulator of claim 53, wherein thestimulating currents flow through substantially parallel and spacedapart conductive elements in a base portion of the magnetic stimulator.55. The magnetic stimulator of claim 53, wherein the return pathcurrents flow through conductive elements of the magnetic stimulatorthat extend away from the external surface of the body part.
 56. Anelectrically conductive coil for placing externally of the skull of asubject and operable to induce currents within the brain of the subject,comprising: a base portion, the base portion configured to provide aflow of electricity, thus producing a magnetic field in a region of thebrain; and an extension portion for providing a return path for the flowof electricity through the base, the extension portion configured toplace electrical currents flowing through the return path away from theregion of the brain having the produced magnetic field, wherein the baseportion comprises multiple substantially parallel and spaced apartstimulating elements configured to conduct electrical current insubstantially a single direction of current flow, thereby inducingelectrical fields within the region of the brain.
 57. The electricallyconductive coil of claim 56, wherein the extension portion comprisesmultiple return elements for respective return paths for the current inthe stimulating elements.
 58. The electrically conductive coil of claim57, wherein the multiple return elements are spaced from the stimulatingelements so that the electrical effect of the return path current on thebody part is reduced.
 59. The magnetic stimulator of claim 56, furthercomprising a power supply electrically connected to the coil.
 60. Themagnetic stimulator of claim 56, wherein the coil comprises a pluralityof windings.
 61. A magnetic stimulator for placing externally of thecranium of a subject and operable to induce currents within the body,comprising: an electrically conductive coil comprising a base portionand an extension portion, the base portion having a width axis and alength axis, and a concave first side configured to be complementary tothe cranium of a subject, the extension portion projecting outwardlyfrom the base portion, the coil in the base portion comprising elementsspaced apart and transverse to the length axis such that the flow ofcurrent in these elements is in substantially the same direction; and ashield at least partially enclosing the extension portion.
 62. Themagnetic stimulator of claim 61, wherein the base portion is a partiallytoroidal or ovate base and is substantially arcuate along its lengthaxis and is substantially arcuate along its width axis.
 63. The magneticstimulator of claim 62, wherein the base portion has an arch lengthalong the length axis from 10 to 50 centimeters.
 64. The magneticstimulator of claim 62, wherein the base portion has an arch lengthalong the width axis in a range from 2 to 15 centimeters.
 65. Themagnetic stimulator of claim 61, wherein the base portion comprisesplural longitudinally-extending laterally spaced frame members.
 66. Themagnetic stimulator of claim 65, wherein at least two of thelongitudinally-extending laterally spaced frame members are in asubstantially non-parallel orientation.
 67. The magnetic stimulator ofclaim 61, wherein the extension portion is positioned off-centerrelative to the base portion.
 68. A magnetic stimulator for placingexternally of the cranium of a subject and operable to induce currentswithin the body, comprising: an electrically conductive coil comprisinga base portion and an extension portion, the base portion having a widthaxis and a length axis, and a concave first side configured to becomplementary to the cranium of a subject, the extension portionprojecting outwardly from the base portion, the coil in the base portioncomprising elements spaced apart and transverse to the length axis suchthat the flow of current in these elements is in substantially the samedirection; and a cushion coupled to the base portion.
 69. The magneticstimulator of claim 68, wherein the transverse elements are arcuate. 70.A method for magnetically stimulating a region of the brain of asubject, the method comprising: providing at least one current pulsethrough a plurality of stimulating pathways that are spaced apart fromone another and configured to orient electrical current in a firstdirection, the stimulating pathways being complementary to the outersurface of the cranium of the subject and adjacent to the region of thebrain being stimulated; and positioning electrical current that flows ina second direction opposite to the first direction away from thestimulating pathways so that the electrical effect of the currentflowing in the second direction on the region of the brain beingstimulated is reduced, wherein the electrical current flowing in thesecond direction flows through pathways that are removed from thesurface of the cranium of the subject.
 71. The method of claim 70,further comprising providing a first pulse of electrical current througha first subset of the stimulating pathways at a first time and providinga second pulse of electrical current through a second subset of thestimulating pathways at a second time after the first time.